1. Field of the Invention
The invention relates to an apparatus for forming thermoplastic laminate into a predetermined configuration.
2. Description of the Related Art
Known devices for forming thermoplastic composite parts include devices using matched mold tools for surrounding the laminate which are placed under pressure, or heat and pressure, by presses or autoclaves.
One of the problems with this type of forming device is that autoclave operation is slow and costly. Another problem is that the tooling of the matched molds is costly. Still another problem with these devices is that the size of the mold tools, and therefore of the part being formed, is restricted by the size of the press or autoclave that is used to operate the matched mold tools.
Another known type of forming device is one in which heated thermoplastic laminate is passed through a series of pressure rollers which shape the bare laminate. Although roller-type devices have historically been used to form sheet metal parts, they have only recently been used to form thermoplastic laminate parts.
One of the problems with the known roller-type forming devices is that gaps are created between the rollers along the roller series where pressure is not maintained on the laminate. The lack of a continuous forming pressure exerted on the laminate as it moves through the rollers negatively affects the integrity of the formed part.
Additionally, since the laminate is exposed to the atmosphere between rollers, it cools unevenly. That is, the convective cooling that takes place between the laminate and the atmosphere is slow compared to the rapid conductive cooling that occurs between the laminate and the rollers, which are generally made of steel or aluminum. Thus, the lack of a continuous forming pressure and the relatively uneven cooling of the laminate tends to cause the laminate to be formed in a semi-compacted state that does not represent the desired shape of the part.
Another problem with this known roller-type forming device is that introducing the bare laminate to the rollers causes the individual plies of laminate to drape around the rollers, causing a bunching together of the laminate and resulting in an unevenly formed part.
Another known roller-type forming device includes a series of pairs of transitional rollers which progressively shape the laminate to the desired shape. Plates made of aluminum or steel that are used with the transitional rollers start out as generally flat plates and are progressively deformed by the transitional rollers. The profiles of the roller pairs change slightly along the series, becoming closer and closer to the ultimate shape, for progressively shaping the plates and the laminate. One problem with this method for forming a shaped part is that the transitional rollers must be individually designed and tooled since each set of rollers has a slightly different profile. Another problem is that the plates used with the transitional rollers must be replaced after each part is made due to the deformation to the plates caused by the transitional rollers.